1. Field of the Invention
This invention relates to chain-extended poly(bis-azidomethyloxetane) energetic thermoplastics. This invention also relates to combustible cartridge cases for high performance direct-fire and indirect-fire ammunition, such as artillery and mortar rounds, and in particular to combustible cartridge cases comprising the chain-extended poly(bis-azidomethyloxetane) energetic thermoplastics.
2. Background of the Invention
Traditionally, weaponry cartridge cases were made of metals such as brass and steel. The selection of metallic materials made the cases resistant to high pressures produced in the cartridge chamber during firing. However, as outlined in U.S. Pat. No. 3,749,023 to Kawaguchi et al., metallic cartridge cases possess several disadvantages. For example, metals are relatively expensive. Further, spent metallic cartridge cases are thermally conductive, and, hence, remain relatively hot subsequent to firing of the loaded ammunition. Thus, great care must be exercised in handling of emptied metallic cartridge cases. Furthermore, it has been reported that the firing of ammunition having metallic cartridge cases can produce toxic gases, thus endangering the marksman.
To address the problems associated with metallic cartridge cases, most current combustible cartridge cases are made from combustible thermosetting materials. For example, the use of nitrocellulose is disclosed in U.S. Pat. No. 3,987,731 to Brzuskiewicz. Advantageously, combustible elements decompose by burning when the ammunition is fired, thus providing additional energy to propel the ammunition and obviating the need to eject and handle hot emptied cartridge cases after firing. Also, nitrocellulose-base cartridge cases possess lower weight and are less expensive than metallic cartridge cases. Disadvantageously, however, the fabrication of nitrocellulose cartridge cases is complex. Further, cartridge cases not meeting specifications or otherwise designated for scrap cannot be recycled by heating, but must be disposed of, typically by burning.
Thus, it would be a significant improvement in the art to design an ammunition case that combusts without generating contaminated waste, and that can be recycled by a simple re-heating process so as to lessen scrap waste disposal.
It is, therefore, an object of this invention to provide an ammunition case that fulfills the above-mentioned improvement in the art.
In accordance with the principles of this invention, the above and other objects are attained by a combustible cartridge case comprising at least one energetic binder derived from, as an ingredient prior to chain extension, poly(bis-azidomethyloxetane) prepolymer blocks (also referred to herein as xe2x80x9cpoly(BAMO) blocksxe2x80x9d or xe2x80x9cpolyBAMO pre-polymer blocksxe2x80x9d) terminated with isocyanate-reactive groups, such as hydroxyl groups. In one embodiment of the invention, a suitable linking system is used to link the poly(BAMO) blocks with each other for forming a chain-extended poly(BAMO) homopolymer. In another embodiment of the invention, using the linking system the poly(BAMO) blocks are linked to one or more prepolymer blocks, other than the BAMO prepolymer blocks, terminated with isocyanate reactive groups for forming a chain-extended poly(BAMO) copolymer or terpolymer. The linking system comprises diisocyanates for end-capping the prepolymer blocks, and a difunctional linking compound. The two functional groups of the difunctional linking compound are reactive with an isocyanate moiety of the diisocyanate for linking the end-capped prepolymer blocks and forming the chain-extended poly(BAMO).
Advantageously, the poly(BAMO) energetic thermoplastic of this invention can be pressed, extruded, rotational molded, injection loaded, or otherwise shaped into a desired configuration. The poly(BAMO) energetic thermoplastic also possesses mechanical, safety, and combustion characteristics that are highly compatible for use as a cartridge case. Another advantage of the novel poly(BAMO) energetic thermoplastic cartridge is its inherently safety. Although the energetic thermoplastic cartridge is highly energetic and burns rapidly at elevated pressures due to the presence of two azido moieties in each BAMO monomer unit, the energetic thermoplastic is sufficiently stable so that combustion is not sustained at room temperature or normal ambient pressures. Yet another advantage of the poly(BAMO) energetic thermoplastic cartridge case is that the thermoplastic can be recycled by melting, thus making the inventive cartridge case more efficient to recycle than conventional thermosets and eliminating scrap waste.
It is another object of this invention to provide an energetic thermoplastic material that is without a xe2x80x9csoftxe2x80x9d (non-crystalline) block so that the energetic thermoplastic material possesses high crystallinity and high density, yet has sufficient elasticity and strength to permit the material to be used as a combustible cartridge case, as well as for other propellant, explosive, and pyrotechnical applications. In accordance with this object, (bis-azidomethyloxetane) prepolymer blocks terminated with isocyanate-reactive groups are linked with a suitable linking system to form a chain-extended poly(BAMO) homopolymer. Chain-extended poly(BAMO) is extremely tough compared to other energetic thermoplastic elastomers, and has a high modulus and high stress at failure. Additionally, chain-extended poly(BAMO) behaves as a viscous liquid when heated above its melting point, thus offering attractive processing and disposal properties. As a consequence, chain-extended poly(BAMO) binder can be dissolved in appropriate solvents, and can be easily mixed with or separated from other energetic ingredients, such as oxidizers, plasticizers, and fuels.
Other objects, aspects, and advantages of this invention will become more apparent to those skilled in the art upon reading the specification and appended claims which, when taken in conjunction with the accompany drawings, explain the principles of this invention.